This invention relates to image converter systems and, more particularly, to a dual visible-to-infrared dynamic image converter system utilizing liquid crystal light valves to provide especially rapid switching, improved efficiency, and application over longer wavelengths.
A visible-to-infrared dynamic image converter is a device which transforms dynamically-changing visible scenes to infrared images of those scenes. Such converters have many uses. One of these uses is in target simulation systems used for nondestructive testing of infrared homing devices. In prior art simulation systems, thin-film material is illuminated with a high intensity beam of visible light containing useful information. The film heats locally at the high intensity points and emits an infrared power pattern related to the spatial information presented by the high intensity visible input beam. These thermal based systems suffer from low resolution caused by thermal spread in the image plane, slow response caused by large thermal time constants, and a limited dynamic range.
A visible-to-infrared dynamic image converter has been disclosed by U. Efron et al, "The Silicon Liquid Crystal Light Valve," Journal of Applied Physics 57, Feb. 15, 1985, which utilizes a cathode ray tube or computer image generator to provide visual images to activate a visible-light sensitive photoconductor coupled with an oxide layer to form an MOS structure. The photoactivated carriers reduce the resistance of the silicon and cause a spatial voltage pattern corresponding to the visible input light intensity to be transferred to a liquid crystal film which creates a highly resolved spatial electric field pattern. The intensity of an infrared beam is modulated in accordance with this pattern to produce a non-thermal image which gives high resolution and fast response while having low power requirements and allowing direct addressing by computer image generation systems.
Such a system, although a substantial improvement over the thermal sensing systems used for testing of infrared homing devices, would be more useful if it were able to provide more rapid switching, had higher efficiency, and could be used over a greater range of wavelengths.